The present invention is in the field of electronic devices, especially piezoelectric devices. More particularly, the present invention is directed to a piezoelectric resonator, for example, which is provided with a radioactive power source to, preferably, make it either self-sustaining or to provide it with larger amplitude response.
Significant advances have been made in the area of piezoelectric resonators in recent years. Single crystal quartz resonators, for example, have particularly low phase noise and, when operating at or near resonance, have greatly reduced power requirements. Still, the demanding applications of space travel where the resonator functions as a timing device upon which other electronics rely, even lower phase noise is desirable as well as reducing consumption of external power.
Accordingly, it is an object of the present invention to utilize a radioactive power source, such as a beta emitter (Nickel 63, for example) on at least one of the electrode leads of the piezoelectric resonator to reduce phase noise as well as the external power required. Given the long half-life of this material and the low power required by a single quartz crystal vibrating at resonance, the self-powered crystal resonator of the present invention can meet the extremely rigorous demands of space travel for extended (i.e., 50+ years) space missions on manned and unmanned space vehicles.
Piezoelectric crystal resonators, in addition to having intrinsically high Q factors, have extremely low impedance (i.e., Ohmic resistance) when operating at its resonant frequency. As a result, these resonators are desired for use as RF filters, sensors, timers, etc. When operating at resonance, the piezoelectric crystal will draw current from the radioactive power source. When operating at any other frequency, the power source will saturate the conductors without producing any current flow. In the case of a piezoelectric crystal being used as a transducer with stationary polarity, or in “piezoelectric ceramics or polymers” which exhibit the phenomenon of electrostriction (i.e., induced piezoelectric properties), the electrical flow can be established using different work function metals. However, in the current invention when used with a radioactive power source, the electrostriction materials function like a capacitor accumulating energy from the power source and releasing on demand.
The chief benefit of the present invention is that it removes application restrictions imposed by intrinsic properties of the materials. Prior attempts to solve these limitations include use of very high drive levels for the resonators and certain dual crystal systems which are more complex and have higher power requirements. By using the anisotropic properties of the single quartz crystal, a resultant electrical response can be selected from a variety of electrical responses based on the angle at which the crystal is cut from the blank.
The manufacturing steps for the present resonator include cleaning the cleaning/etching the surface with chemicals to ready the base plate. Then the electrodes, typically gold, silver, platinum or aluminum, are deposited on one of the surfaces using vacuum deposition. At this point, the deposition has reduced the operating frequency by typically 1% from the nominal frequency of the unprocessed resonator. The base plated device can now mounted in its holder, coated with the beta emitter and its operational properties tweaked to the final desired frequency. The beta emitter is applied, most preferably, using vacuum deposition. The resonator is then subjected to a high vacuum or an inert atmosphere and sealed in its housing.
The crystal resonator of the present invention will be designed to operate at its resonant frequency which has the lowest possible impedance for the resonator. Once the initial RF signal is applied to initiate vibration, the radioactive power source can sustain the vibration with some additional amplitude of the output signal. To maintain the oscillation, the RF is returned to the feedback loop of the circuit, and the additional energy (excess amplitude) can be stored for future use or removed from the system. In some instances, the excess amplitude will be allowed to remain in the system to lower the effective phase noise thereof and improve resolution. The radioactive power source can also be tapped by supplemental circuitry to recharge batteries or provide energy to inaccessible power sources. The actual amount of excess energy that can be tapped from the radioactive source will depend on the power density and the existing level at the time of tapping (the most current quasi-constant if a long half-life isotope is used).
The piezoelectric circuit of the present invention comprises a) a piezoelectric resonator; b) electrodes formed on the piezoelectric resonator, the electrodes being used to actuate vibration of the piezoelectric resonator; c) a radioactive power source associated with at least one of the electrodes of the piezoelectric resonator; whereby the piezoelectric circuit requires a reduced external power source. The power source is preferably a radioactive layer which is associated with the at least one electrode and is applied by electroplating or vacuum deposition. Most preferably, the radioactive power source is a beta emitter such as Nickel 63 and the resonator is a quartz crystal. For some applications, the quartz crystal will be associated with an Application Specific Integrated Circuit (ASIC) substrate. In some instances the size of the radioactive power source is selected to make the piezoelectric resonator self-sustaining. In other instances, the size is selected to provide the piezoelectric resonator with a larger amplitude response than it would otherwise be able to obtain.
Various other features, advantages, and characteristics of the present invention will become apparent after a reading of the following detailed description.